A conventional resistor is, for example, a ceramic resistor having axial leads on both sides, thereafter, different types of surface mount chip resistors are fabricated by thick film printing process, which mainly perform a series of processes including a printing process, a laser-modification process, a process for forming copper electrode ends, and an electroplating process in order to form a desired resistor on a selected ceramic substrate.
In addition, an alloy transistor is also used widely. However, as shown in FIG. 3, when the alloy transistor is made by a traditional thick film printing process, the printing process has directional limitation. If the printing direction is not paid more attention during the printing process, it is easily to fail to form a ring-shaped insulating layer 36 which can cover an insulating cover area 323 of an alloy resistor unit 32 during the printing process of the insulating layer 36. Therefore, the product yield decreases.
To solve above problem, a method for forming an insulating layer by spray coating process is provided. However, when the surface of the insulating layer which is formed by spray coating process is not uniform or the workpieces has a dead angle, the subsequent surface adhesion process will be affected. In addition, in spray coating process, since the spray coating material has a lower flash point, the temperature control should be paid much attention to its surroundings for avoiding a process risk. Also, the dryness of spray particles and the dust control are key factors to influence the product quality during the spray process. Furthermore, there is a method for forming the insulating layer such as epoxy resin by a press molding. However, if various appearances of alloy resistors are required, an additional mold will be necessary to fabricate, and in addition, the remained excess epoxy resin in mold channels often adhered to workpieces which has to be removed. Thus, the increased working hours for removing the excess epoxy resin and the additional expenses of fixtures and equipments may lead to inconvenient processes and reduce the cost advantage.
Therefore, it is a necessary to develop an easy and efficient manufacturing method capable of obtaining an alloy resistor having an insulating layer with a smooth surface under the existent process.